The disclosure relates to a projection exposure apparatus for semiconductor lithography comprising a plurality of optical elements and a damping element for damping mechanical vibrations, and to a changeable assembly for a projection exposure apparatus for semiconductor lithography. Furthermore, the disclosure relates to a measuring assembly for a projection exposure apparatus. In this case, the mechanical vibrations discussed generally lead to impairments of the optical imaging quality of the systems discussed, said impairments being manifested for example as a loss of contrast and impairing the yield of semiconductor products having entirely satisfactory quality. The problem area mentioned is also aggravated in particular by the fact that during the lifetime of a projection exposure apparatus for semiconductor lithography, the process parameters with which the apparatus is operated are changed a number of times. By way of example, exposure times or advancing speeds of reticle and wafer stage change. The dynamic behaviour of the projection objective is not unaffected by these changes. Thus—depending on the process parameters mentioned—varying optical elements in the projection exposure apparatus are excited to effect natural vibrations. This makes it considerably more difficult for the damping system of a projection exposure apparatus to be designed optimally with regard to all possible use parameters from the outset.